Studies are being conducted on the immunologic mechanisms responsible for the elimination of blood stream Dipetalonema viteae microfilariae (mf) in infected hamsters. Quantitative infections can be established in hamsters by surgical implantation of adult worms in the recipient's subcutis. Bloodstream mf appear in the recipient within 3 days of transfer and reach a maximum after 20 days. This level is maintained for 15-20 days before declining to zero 60 days post transfer. Remission of the microfilaremia resulted from passive immunization with serum from hyperinfected hamsters but not with normal or single infection serum. Hamsters were vaccinated with preparations of homogenized female worms, male worms, mf or saline and challenged with 100 adult worms. The microfilaremia in hamsters receiving the female work vaccine was significantly reduced and transient compared with saline controls. The male worm and mf vaccine gave no protection. The dynamics of D. viteae infection in the inbred hamster strains LSH/LAK, LHC/LAK, CB/LAK, MHA/LAK and PD4/LAK, were compared with random bred hamsters, Lak/LVG. Parasite antigens were separated by isoelectric focusing on flat beds of Ultrodex gels and on polyacrylamide gels. The immunogenicity of the parasite antigen fractions was studied by crossed immunoelectrophoresis, radioimmunoassay, blast transformation and skin sensitivity. The amicrofilaremic state was reversed when infected hamsters were treated with prenisolone acetate or cyclophosphamide. BIBLIGRAPHIC REFERENCES: Neilson, J.T.M., 1977. Immunity to Dipetalonema viteae in inbred and random bred strains of golden hamsters. J. Parasit. Neilson, J.T.M., 1977. Amicrofilaremia in hamsters infected with Dipetalonema viteae and reversal by immunosuppression. Amer. J. Trop. Med. Hyg.